214 Annals of the /South African Museum. 



This is reminiscent of the sphenethmoid surrounding the anterior 

 part of the brain in Pareiasaurus described by Watson. Un- 

 fortunately, the complete course of the bone is not seen ; the 

 bony walls of the cylinder are very thin. The anterior prolongation 

 of the basisphenoid is sheathed by the inverted V-shaped bone, 

 which may be formed of the ascending plates of the pterygoid. 



General Considerations. Taken in conjunction with the accounts 

 already published of the brain-case in Dimetrodon and Diademodon 

 and its allies, this study shows that in the essentials of structure 

 there is a striking similarity throughout the whole of the carnivorous 

 Therapsida. All have the inner ear lying well down in the brain 

 in many cases the vestibule pierces the floor and not up in the 

 side-wall, thus showing a mammalian affinity rather than one 

 with modern reptiles. In this respec't, the Dinocephalia seem to 

 be quite as far advanced as forms like Diademodon from much 

 higher zones. 



It can be seen that the Gorgonopsia at least as far as the 

 larger types are concerned do not approximate so closely to the 

 Cynognathidae as a study of their external characters would 

 indicate. In the first place the sloping, sometimes almost vertical, 

 wall separating the posterior part of the brain from the hypophysis 

 and pierced by the foramen for the Vlth nerve finds no counter- 

 part in Diademodon nor in the Therocephalia from the lower zones, 

 where one simply finds the lateral portions remaining as processi 

 inferiores anteriores prooticorum, separated by a deep notch 

 whose base does not lie above the level of the bottom of the foramen 

 magnum. In Dimetrodon, however, a similar transverse wall is 

 seen, and in the Dinocephalia it may be present in some forms. 

 Further, the epipterygoid in the Gorgonopsia as in the Dinocephalia 

 is a rod-like bone with an expanded base ; whereas in Diademodon 

 and in at least some of the Therocephalia it is a plate. 



Thus the Gorgonopsia seem to be more closely allied to the 

 Pelycosauria and Dinocephalia than to any other sub-orders. 

 This relationship has previously been noted by Broom and others 

 from a study of the external characters ; and it is important to 

 find that evidence from the brain-case affirms their conclusions. 

 It is unfortunate that no investigations have yet been made upon 

 the Gorgonopsia such as Galesuchus gracilis from the lowest portion 

 of the Beaufort Beds ; but the palatal portion of a medium-sized 

 Scymnof/nathus ? from the Endothiodon zone of Beaufort West 

 accords well with the larger forms from higher up. 



